• Reproduction is the process by which living organisms produce new individuals similar to themselves. It ensures continuity of life on earth.
  • Nucleus of the cell contains DNA (Deoxyribose Nucleic Acid) which is the hereditary material.
  • DNA replicates and forms new cells causing variation. So, these new cells will be similar but may not be identical to the original cell.
  • Variations are useful for the survival of the individual and species over time as well as the basis for evolution.

TYPES OF REPRODUCTION

ASEXUAL REPRODUCTION

  • A single individual gives rise to a new individual.
  • Gametes are not formed.
  • New individual is identical to the parent.
  •  It is extremely useful as a means of rapid multiplication.
  • Adopted by lower organisms.

SEXUAL REPRODUCTION

  • Two individuals i.e., one male and one female are needed to give rise to new individuals.
  • Gametes are formed.
  • New individual is genetically similar but not identical to their parents.
  • It is useful to generate more variations in species.
  • Adopted by higher organisms.

MODES OF ASEXUAL REPRODUCTION

(i) Fission

The parent cell divides into daughter cells.
(i)Binary fission: 2 cells are formed. Example: amoeba.                                  (ii)Multiple fission: Many cells are formed. Example: Plasmodium. 

(ii) Fragmentation

The organism breaks-up into smaller pieces upon maturation, each piece develops into a new individual. Example: Spirogyra.

(iii) Regeneration

If an organism is somehow cut or broken into many pieces, each piece grows into a complete organism. Example: Planaria, Hydra.

(iv) Budding

A bud is formed which develops into a tiny individual. It detaches from the parent body upon maturation and develops into a new individual. Example: Hydra

(v) Vegetative Propagation

In many plants, new plants develops from vegetative parts such as:
• By roots: Example: dahlias, sweet potato. 
• By stem: Example: potato, ginger. 
• By leaves: Example: bryophyllum (leaf notches bear buds which develop into plants). 

Artificial Methods in Vegetative Propagation

  • Grafting: Example: Mango
  • Cutting: Example: Rose
  • Layering: Example: Jasmine
  • Tissue culture: New plants are grown by using the growing tip of a plant. These growing cells are kept in a culture medium that leads to the formation of calluses. Callus is then transferred to the hormone medium which causes growth and differentiation. Example: ornamental plants, orchids.
  • Benefits of tissue culture :We can grow plants like banana, rose, jasmine etc. that have lost the capacity to produce seeds. New plants are genetically similar to parents. Helps in growing seedless fruits.
  • Spore Formation: Spores are small bulb-like structures which are covered by thick walls. Under favourable conditions, they germinate and produce new organisms. Example: Rhizopus.   

SEXUAL REPRODUCTION

  • When reproduction takes place as a result of the fusion of male and female gametes is called sexual reproduction.
  • Fusion of gametes is called fertilization which results in variation.

SEXUAL REPRODUCTION IN PLANTS

  • Flowers are the reproductive organs of plants.
  • A typical flower consists of four main whorls namely sepals, petals, stamen and pistil.

Types of Flowers

  • Bisexual flower: Both male and female reproductive parts are present.
    Example: Hibiscus, mustard.
  • Unisexual flower: Either male or female reproductive part is present. Example: Papaya, watermelon.

Structure of Flower

Process of Seed Formation

  • Pollen grains, produced in the anther, are transferred to the stigma of the same flower (self pollination) or stigma of another flower (cross pollination) through agents like air, water or animals.
  • Pollen grains germinate and form pollen tubes which pass through style to reach upto the ovules present in ovary.
  • The fusion of male and female gametes is called fertilization. Zygote is produced inside the ovary.
  • Zygote divides to form embryos. Ovule develops thick coat and changes into seed gradually.
  • Ovary changes into fruit and other parts of the flower fall off.
  • The seed germinates to form a plant under suitable conditions such as air, moisture etc.

How do Organisms Reproduce?

  • Humans use sexual mode of reproduction.
  • Sexual maturation: The period of life when production of germ cells i.e. ova (female) and sperm (male) start in the body. This period of sexual maturation is called puberty.

CHANGES AT PUBERTY

  • Common in male and female
    (i) Thick hair growth in armpits and genital area.
    (ii) Skin becomes oily, may result in pimples.
  • In girls
    (i) Breast size begin to increase.
    (ii) Girls begin to menstruate.
  • In boys
    (i) Thick hair growth on face.
    (ii) Voice begin to crack.
  • These changes signals that sexual maturity is taking
    place.

MALE REPRODUCTIVE SYSTEM

(i) Testes

  • A pair of testes are located inside the scrotum which is present outside the abdominal cavity.
  • Scrotum has a relatively lower temperature needed for the production of sperms.
  • Male germ cells i.e. sperms are formed here.
  • Testes release male sex hormone (testosterone).
  • Function of testes:
    (i) Regulate production of sperm.
    (ii) Bring changes at puberty.

(ii) Vas deferens

  • Regulate production of sperm.
  • Bring changes at puberty.

(iii) Urethra

It is a common passage for both sperms and urine. Its outer covering is called penis.

(iv) Associated Glands

  • Seminal vesicles and prostate glands add their secretion to the sperms. This fluid provides nourishment to sperms and makes their transport easy.
  • Sperm along with secretion of glands form semen.

FEMALE REPRODUCTIVE SYSTEM

(i) Ovary

  • A pair of ovaries is located on both sides of the abdomen.
  • Female germ cells i.e. eggs are produced here.
  • At the time of birth of a girl, thousands of immature eggs are present in the ovary.
  • At the onset of puberty, some of these eggs start maturing.
  • One egg is produced every month by one of the ovaries.

(ii) Oviduct or Fallopian Tube

  • Receive the egg produced by the ovary and transfer it to the uterus.
  • Fertilization i.e. fusion of gametes takes place here.

(iii) Uterus

  • It is a bag-like structure where development of the baby takes place.
  • Uterus opens into vagina through the cervix.

Fertilization of Egg

(a) When egg is fertilized:
  • The fertilized egg called zygote is planted in the uterus and develops into an embryo.
  • The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. It provides a large surface area for the exchange of glucose, oxygen and waste material.
  • The time period from fertilization up to the birth of the baby is called gestation period. It is about 9 months.
(b) When egg is not fertilized:
  • The uterus prepares itself every month to receive fertilized eggs.
  • The lining of the uterus becomes thick and spongy, required to support the embryo.
  • When fertilisation has not taken place, this lining is not needed any longer.
  • This lining breaks and comes out through vagina as blood and mucus.
  • This cycle takes around 28 days every month and is called menstruation. 

REPRODUCTIVE HEALTH

Reproductive health means a total well-being in all aspects of reproduction i.e. physical, emotional, social and behavioural.

Sexually Transmitted Diseases(STDs)

  • Many diseases can be sexually transmitted such as:
    (i) Bacterial : Gonorrhea and syphilis
    (ii) Viral : Warts and HIV-AIDS
  • Use of condoms prevents these infections to some extent.
  • Contraception: It is the avoidance of pregnancy, which can be achieved by preventing the fertilization of ova.

Methods of Contraception

(i) Physical barrier
a. To prevent the union of egg and sperm.
b.  Use of condoms, cervical caps and diaphragm.
(ii) Chemical methods
a.  Use of oral pills
b. These change hormonal balance of the body so that eggs are not released.
c.  May have side effects.
(iii) Intrauterine contraceptive device (IUCD)
a. Copper-T or loop is placed in the uterus to prevent pregnancy.
(iv) Surgical methods
a. In males the vas deferens is blocked to prevent sperm transfer called vasectomy.
b. In females, the fallopian tube is blocked to prevent egg transfer called tubectomy.

Female Foeticide

  • The practice of killing a female child inside the womb is called female foeticide.
  • For a healthy society, a balanced sex ratio is needed that can be achieved by educating people to avoid malpractices like female foeticide and prenatal sex determination.
  • Prenatal sex determination is a legal offence in our country so as to maintain a balanced sex ratio.
  • All the living organisms respond and react to changes in the environment around them.
  • The changes in the environment to which the organisms respond and react are called stimuli such as light, heat, cold, sound, smell, touch etc.
  • Both plants and animals respond to stimuli but in a different manner.

SYSTEMS FOR CONTROL AND COORDINTION IN ANIMALS

  • Control and Coordination in animals is done with the help of two main systems: 
    (i) Nervous system 
    (ii) Endocrine system 

NERVOUS SYSTEM

  • Control and coordination are provided by nervous and muscular tissues.
  • Nervous tissue is made up of an organized network of nerve cells or neurons which is specialized for conducting information via electrical impulses from one part of the body to another.

RECEPTORS

  • These are specialized tips of some nerve cells that detect the information from the environment. 
  • These are located in our sense organs.
    (i) Ear: It acts as phonoreceptors (receiving sound). It helps in hearing and maintaining the balance of the body. 
    (ii) Eyes: It acts as photoreceptors (receiving light). It helps in seeing 
    (iii) Skin: It acts as a thermoreceptors (feels temperature). It helps in feeling heat or cold and touch. 
    (iv) Nose: It acts as olfactory receptors (sense of smell). It helps in the detection of the smell. 
    (v) Tongue: It acts as a Gustatory receptors (sense of test). It helps in the detection of taste. 

NEURON

  • It is the structural and functional unit of the nervous system.

Functioning of Neuron

  • The information from receptors is acquired at the end of the dendritic tip of a nerve cell as a chemical reaction that creates an electrical impulse.
  • This impulse travels from the dendrite to the cell body and then at the end of the axon.
  • Chemicals are released at the end of the axon by the effect of electrical impulse.
  • These chemicals cross the gap (synapse) and start a similar electrical impulse in a dendrite of the next neuron.
  • The similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscle cells or gland.

Parts of Neuron

  • Dendrite: It acquires information.
  •  Cell body: The information acquired by it travels as an electrical impulse.
  • Axon: It is the longest fibre on the cell body called an axon. It transmits electrical impulses from the cell body to the dendrite of the next neuron. 

SYNAPSE

  • It is the gap between the nerve ending of one neuron and dendrite of the other neuron. Here, the electrical signal is converted into a chemical signal for onward transmission.

REFLEX ACTION

  • Reflex action is a quick, sudden and immediate response of the body to a stimulus. Example: Knee jerk, withdrawal of hand on touching hot object.
  • Stimulus: It is an observable or detectable change in the external or internal environment to which an organism reacts.
  • Reflex arc: The pathway through which nerve impulses pass during reflex action is called reflex arc.

  • Response: It is the final reaction after the reflex action. 

THREE TYPES OF RESPONSES

  • Voluntary: Controlled by fore brain. Example: talking, writing. 
  • Involuntary: Controlled by mid and hind brain. Example: heart beat, vomiting, respiration. 
  • Reflex action: Controlled by spinal cord. Example: withdrawal of hand on touching a hot object. 

NEED FOR REFLEX ACTIONS

  • In some situations such as touching a hot object, pinching etc. we need to act quickly, otherwise our body would be harmed. Here response is generated from the spinal cord instead of the brain. In this way, time for taking action is reduced which saves us from injury.

HUMAN NERVOUS SYSTEM

  • Human nervous system consists of two parts, Central nervous system (CNS) and Peripheral nervous system (PNS).
  • Central nervous system consists of Brain and Spinal Cord.
  • Peripheral nervous system consists of Cranial Nerves which arise from the brain and Spinal Nerves which arise from the Spinal cord.

HUMAN BRAIN

  • Brain is the main coordinating centre of the body. It has three major parts:
    (i) Fore-brain (ii) Mid-brain (iii) Hind-brain

(i) Fore-brain

  • It is the most complex or specialised part of the brain. It consists of cerebrum.
  • Functions of the Fore-brain:
    (i) Thinking part of the brain.
    (ii) Control the voluntary actions.
    (iii)Store information (Memory).
    (iv) Receives sensory impulses from various parts of the body and integrate it.
    (v) Centre associated with hunger.

(ii) Mid-brain

  • Controls involuntary actions such as change in pupil size and reflex movements of head, neck and trunk.

(iii) Hind-brain

  • It has three parts:
    (i) Cerebellum : Controls posture and balance. Precision of voluntary actions. Example: picking pen. 
    (ii) Medulla : Controls involuntary actions. Example: blood pressure, salivation, vomiting. 
    (iii) Pons : Involuntary actions, regulation of respiration. 

PROTECTION OF BRAIN AND SPINAL CORD

  • Protection of the Brain: Brain is protected by a fluid filled balloon which acts as a shock absorber and is enclosed in the cranium (skull or brain box).
  • Protection of Spinal Cord: Spinal cord is enclosed in the vertebral column.

COORDINATION BETWEEN NERVOUS AND MUSCULAR TISSUE

  • For taking place voluntary actions, the brain has to send messages to muscles.
  • The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system consisting of cranial nerves arising from the brain and spinal nerves arising from the spinal cord.
  • The brain thus allows us to think and take actions based on that thinking. This is accomplished through a complex design, with different parts of the brain responsible for integrating different inputs and outputs.

LIMITATIONS OF ELECTRIC COMMUNICATION/NERVOUS SYSTEM

  • Electric impulse will reach only to those cells that are connected by nervous tissue. 
  • After generation and transmission of an electrical impulse, the cell takes some time to reset its mechanism before transmitting another impulse. So cells cannot continually create and transmit impulse. 
  • Plants do not have any nervous system. 

CHEMICAL COMMUICATION

  • It helps in overcoming the limitations of electric communication.

COORDINATION IN PLANTS

  • There are two types of movements in plants. 
    (i) Independent of growth 
    (ii) Dependent on growth 

(i)Independent of Growth

  • Independent growth has an immediate response to the stimulus.
  • Plants use electrical-chemical means to convey information from cell to cell.
  • For movement to happen, cells change their shape by changing the amount of water in them, resulting in swelling or shrinking of cells. Example: Drooping of leaves of ‘Touch-me-not’ plant on touching it.

(ii)Dependent on Growth

  • These movements are tropic movements i.e., directional movements in response to stimulus.
  • Tendrils: The part of the tendril away from the object grows more rapidly as compared to the part near the object. This causes circulating of tendril to circulate around the object.
  • Phototropism: Movement towards light.
  • Geotropism: Movement towards/away from gravity.
  • Chemotropism: Growth of the pollen tube towards ovule.
  • Hydrotropism : Movement towards water.

PLANT HORMONES

  • These are chemical compounds which help to coordinate growth, development and responses to the environment.
  • Main plant hormones are:
    • Auxin: These hormones are synthesized at shoot tip. It helps the cells to grow longer and involved in phototropism (response towards light).          • Gibberellin : It helps in the growth of the stem. 
    • Cytokinins: It promotes cell division. This is present in greater concentration in fruits and seeds 
    • Abscisic Acid: It inhibits growth. It also causes wilting of leaves and is also known as a stress hormone. 

HORMONES IN ANIMALS

  • Hormones are the chemical substances which coordinate the activities of living organisms and also their growth.
  • Endocrine glands : These glands secrete their product (hormone) into the blood and the main organ for releasing the hormones.

LIST OF ENDOCRINE GLANDS

(i) Thyroxine: This hormone is secreted by Thyroid. The Thyroid is located in Neck/Throat region. It regulates the metabolism of carbohydrates, fats and proteins. 
(ii) Growth hormones: This is secreted by the Pituitary (master gland). This gland is located in Mid-brain. It regulates growth and development. 
(iii) Adrenaline: This hormone is secreted by Adrenal. The adrenal gland is located above both kidneys. It regulates blood pressure (increasing), heart beat, and carbohydrate metabolism (during emergencies). 
(iv) Insulin: This hormone is secreted by Pancreas. The pancreas is located below the stomach. It reduces and regulates blood sugar level. 
(v) Sex hormones:
(a) Testosterone in males: This hormone is secreted by testis. The testis is located in genital area. Its changes associated with puberty (Sexual maturity).
(b) Estrogen in females: This hormone is secreted by Ovaries. The ovaries are located in the lower abdomen area. Its changes associated with puberty (Sexual maturity). 

IMPORTANCE OF IODINE

Iodised salt is necessary because iodine is an essential part of the thyroxine hormone secreted by the thyroid gland. Thyroxine regulates metabolism of carbohydrates, fats and proteins. So, we must consume iodised salt which is necessary for proper working of the thyroid gland. It’s deficiency causes a disease called goiter (Swollen neck).

DIABETES

Diabetes is a disease in which blood sugar level increases.

CAUSE OF DIABETES

The disease is caused due to the deficiency of insulin hormone secreted by the pancreas that is responsible for controlling blood sugar levels.

TREATMENT OF DIABETES

Injections of insulin hormone can help in the treatment of diabetes.

FEEDBACK MECHANISM

The excess or deficiency of hormones has a harmful effect on our body. Feedback mechanism makes sure that hormones should be secreted in precise quantities and at the right time. Example: Feedback mechanism to control the sugar level in blood is as follows:

  • Matter around us is present in the form of elements, compounds and mixtures.
  • Elements are substances containing atoms of only one type. E.g., Na, Mg, Au, etc.
  • There are 118 elements known to us. All these have different properties.
  • To make the study of these elements easy, these elements have been divided into few groups in such a way that elements in the same group have similar properties.

DOBEREINER'S TRAIDS

  • When elements are arranged in the order of increasing atomic masses, groups of three elements (known as traids), having similar chemical properties are obtained.
  • The atomic mass of the middle element of the triad was roughly the average of the atomic masses of the other two elements.

LIMITATIONS OF DOBEREINER'S TRAIDS

Only three traids were recognized from the elements known at that time.
(i) Li, Na, K
(ii) Ca, Sr, Ba
(iii) Cl, Br, I

NEWLAND'S LAW OF OCTAVES

  • Newland arranged the then known elements in the order of increasing atomic masses and found that the properties of every 8th element is similar to that of the 1st element.
  • He compared this to the octaves found in music and called it the ‘Law of Octaves’. For example, the properties of lithium (Li) and sodium (Na) were found to be the same.

LIMITATIONS OF NEWLAND'S LAW OF OCTAVES

  • It was applicable upto calcium (for lighter elements only).
  • Properties of new discovered elements did not fit into the law of octave.
  • To fit elements into his table, Newlands put even two elements together in one slot and that too in the column of unlike elements having very different properties.

MENDELEEV'S PERIODIC TABLE

  • When elements are arranged in the order of increasing atomic masses, the element with similar properties occur at regular intervals.
  • The properties of elements are a periodic function of their atomic masses.
  • Mendeleev’s periodic table is based on the chemical properties of elements. It contains 7 periods (horizontal rows) and 8 groups (vertical columns).

MERITS OF MENDELEEV'S PERIODIC TABLE

  • Some gaps were left for the undiscovered elements like gallium (Ga), Scandium (Sc) and Germanium (Ge).
  • Predict properties of elements on the basis of their positions in the periodic table.
  • Accommodate noble gases when they were discovered without disturbing the original arrangement.

LIMITATIONS OF MENDELEEV'S CLASSIFICATION

  • Position of isotopes could not be explained.
  • No fixed position for hydrogen.
  • Wrong order of atomic masses of some elements could not be explained.

MODERN PERIODIC TABLE

  • Atomic number of an element is a more fundamental property than its atomic mass.
  • According to the Modern Periodic law : The properties of elements are a periodic function of their atomic number.
  • All the anomalies of Mendeleev’s classification disappear.

EXPLANATION OF ANNOMALIES BY MODERN PERIODIC TABLE

  • Explanation for the position of isotopes (Same atomic number put at one place in the same group).
  • Cobalt with atomic number 27 came first and nickel (28) should come later.
  • Unlike atomic masses, an atomic number is always a whole number, so there is no element between hydrogen and helium.
  • Atomic Number: It is denoted by Z and equal to the number of protons in the nucleus of an atom.
  • Modern Periodic table has 18 vertical columns known as ‘groups’ and 7 horizontal rows known as ‘periods’.
  • Elements with the same number of valence electrons are placed in the same group. Example:
    Li : 2, 1
    Na : 2, 8, 1
    K : 2, 8, 8, 1
  • Outermost or valence shell in all the three contains 1 electron. These elements have been placed in the same group.
  • Number of shells increases as we go down the group.
  • Elements with the same number of occupied shells are placed in the same period. For example, Li (2, 1); Be (2, 2); B (2, 3), C (2, 4), N(2, 5). These elements have the same number of shells (two).
  • Each period marks a new electronic shell getting filled.
  • Number of elements placed in a particular period depends upon the fact that how electrons are filled into various shell.
  • Maximum number of electrons that can be filled in a shell is given by 2n2 where n is shell number. Example:
    K shell n = 1 or 2n2 = 2(1) 2 = 2 (First period has 2 elements.)
    L shell n = 2 or 2n2 = 2(2)2 = 8 (Second period has 8 elements.)
  • Position of an element in the periodic table tells us its chemical reactivity.
  • Valence electrons determine the kind and number of bonds formed by the element.

TRENDS IN THE MODERN PERIODIC TABLE

  • Valency: No. of valence electrons present in the outermost shell of its atom. On moving from left to right in each period, the valency of elements increases from 1 to 4 and then decreases to 0. Valency remains the same down in a group.
  • Atomic size: Atomic size refers to the radius of an atom. It may be visualized as the distance between the centre of the nucleus and the outermost shell.
  • Atomic size or radius of an atom decreases as we move from left to right in a period because due to large +ve charge on the nucleus, the electrons are pulled in closer to the nucleus and size decreases.
  • Atomic size increases as we move down the group because new shells are being added and this increases the distance between nucleus and outermost electron.

Metallic Character

  • Metallic character means the tendency of an atom to lose electrons.
  • Metals occupy the left hand side of the periodic table.
  • On moving left to right in a period, the metallic character of an element decreases because the effective nuclear charge increases. It means the tendency to lose electrons decreases.
  • Metals are electropositive as they tend to lose electrons while forming bonds.
  • Metallic character increases as we go down a group as the effective nuclear charge is decreasing.

Non-Metallic Character

  • Non-metals are electronegative as they tend to form bonds by gaining electrons.
  • Non-metals occupy the right side of the periodic table.
  • Non-metallic character increases across a period because due to increase in effective nuclear charge that means tendency to gain electron increase.
  • Non-metallic character decreases as we move down a group due to decrease in effective nuclear charge experienced by the valence electron thus the tendency to gain electrons decreases.
  • In the middle of the periodic table we have semi-metals or metalloids because they exhibit some properties of metals and non-metals.
  • Oxides of metals are basic in nature while oxides of non-metals are acidic in nature.

ATOMIC SIZE, METALLIC CHARACTER AND NON-METALLIC CHARACTER ACCORDING TO THE PERIODIC TABLE

  • Compounds are of two types:
    (i) Organic Compounds
    (ii) Inorganic Compounds
  • Organic Compounds are made up of Carbons and form the basis of all living organisms.

THE COVALENT BOND

  • Carbon always forms a covalent bond.
  • The bond formed by sharing of an electron pair between two atoms are known as covalent atoms.
  • Noble gas configuration of Carbon:                                                            (i)Carbon is tetravalent; it does not form an ionic bond by either losing four electrons (C4+) or by gaining four electrons (C4-). It is difficult to hold four extra electrons and would require a large amount of energy to remove four electrons. So, carbon can form bonds by sharing its electrons with the electrons of other carbon atoms or with other elements and attain a noble gas configuration.                                      (ii)The atoms of other elements like hydrogen, oxygen and nitrogen, chlorine also form bonds by the sharing of electrons.
  • H – H single bond between hydrogen atoms (H2)
  • O = O double bond between oxygen atoms (O2)
  • N ≡ N triple bond between nitrogen atoms
  • Water molecules have a single covalent bond between one oxygen and two hydrogen atoms.

PHYSICAL PROPERTIES OF COVALENT COMPUNDS

  • Covalent compounds have low melting and boiling points as they have weak intermolecular force.
  • They are generally poor conductor of electricity as electrons are shared between atoms and no charged particles are formed
FORMATION OF COVALENT COMPOUNDS

VERSATILE NATURE OF CARBON

  • The two characteristic properties of carbon element which lead to the formation of a large number of compounds :
  • Catenation: Carbon can link with carbon atoms by means of covalent bonds to form long chains, branched chains and closed rings. Compound Carbon atoms may be linked by single, double or triple bonds.
  • Tetravalency: Carbon has 4 valence electrons. Carbon can bond with four carbon atoms, monovalent atoms, oxygen, nitrogen and sulphur.

HYDROCARBON

  • Compounds made up of hydrogen and carbon are
    called hydrocarbons.
  • There are two types of Hydrocarbons.
    (i) Saturated Hydrocarbons
    (ii) Unsaturated Hydrocarbons 

(i) Saturated Hydrocarbons

  • Single bond between carbon atoms.
  •  ᅳCᅳCᅳ
  • Alkanes are saturated hydrocarbons.
  • General Formula: CnH2n+2

(ii) Unsaturated Hydrocarbons

  • Double or triple bond between carbon atoms.
  • Alkenes and Alkynes are unsaturated hydrocarbons.
  • Alkenes: ᅳC=Cᅳ
    General formula: CnH2n
  • Alkynes: ᅳC≡Cᅳ
    General Formula: CnH2n-2

ELECTRON DOT STRUCTURE OF SATURATED HYDROCARBONS

  • Ethane C2H6
  • Names, molecular formulae and structure formulae of saturated hydrocarbons (Alkanes):
STRUCTURE OF ETHANE
EXAMPLES OF SATURATED HYDROCARBONS

ELECTRON DOT STRUCTURE OF UNSATURATED HYDROCARBONS

  • Ethene (C2H4)
  • Ethyne (C2H2)
  • Names, molecular formulae and structure formulae of unsaturated hydrocarbons (Alkenes and Alkynes):
STRUCTURE OF ETHENE AND ETHYNE
EXAMPLES OF UNSATURATED HYDROCARBONS

CARBON COMPOUNDS ON THE BASIS OF STRUCTURE

(i)Straight(unbranched) Chain:

Example: C3H8 ᅳCᅳCᅳCᅳCᅳCᅳ

(ii)Branched:

These three above compounds have the same molecular formula but different structures are called structural isomers and the phenomenon is structural isomerism.

(iii)Cyclic:

Example: C6H12

FUNCTIONAL GROUPS

  • In a hydrocarbon chain, one or more hydrogen atom is
    replaced by other atoms in accordance with their valencies. These are heteroatoms.
  • These heteroatoms or group of atoms which make carbon compound reactive and decides its properties are called functional groups.

HOMOLOGOUS SERIES

  • It is a series of compounds in which some functional group substitutes for the hydrogen in a carbon chain.
  • Example: Alcohols – CH3OH, C2H5OH, C3H7OH, C4H9OH
  • They have the same general formula.
  • Any two homologues differ by – CH2 group and the difference in molecular mass is 14μ.
  • They have the same chemical properties but show gradual change in physical properties.
  • Nomenclature of Carbon Compounds
    (i) Identify the number of carbon atoms in compounds.
    (ii) Functional groups are indicated by suffix or prefix.

CHEMICAL PROPERTIES OF CARBON COMPOUNDS

(i)Combustion

  • Carbon and its compounds are used as fuels because they burn in air releasing a lot of heat energy.
  • Saturated hydrocarbons generally burn in air with a blue and non-sooty flame.
  • Unsaturated hydrocarbon burns in air with a yellow sooty flame because the percentage of carbon is higher than saturated hydrocarbon which does not get completely oxidized in air.

(ii)Oxidation

Alcohols can be converted to carboxylic acid in the presence of oxidizing agent alkaline KMnO4 (potassium permanganate) or acidic potassium dichromate.

(iii)Addition Reaction

Unsaturated hydrocarbons add hydrogen in the presence of catalyst palladium or nickel. Vegetable oils are converted into vegetable ghee using this process.It is also called hydrogenation of vegetable oils.

(iv)Substitution Reaction

Important Carbon Compounds: Ethanol and Ethanoic acid

Physical Properties of Ethanol

  • Colourless, pleasant smell and burning taste.
  • Soluble in water.
  • Volatile liquid with a low boiling point of 351 K.
  • Neutral compound.

Chemical Properties of Ethanol

(i) Reaction with Sodium 
2Na + CH3CH2OH → 2CH3CH2ONa+ + H2 (Sodium ethoxide)
This reaction is used as a test for ethanol by evolution of H2 gas (Burn with pop sound).
(ii) Dehydration 

Physical Properties of Ethanoic Acid

  • Colorless liquid has a sour taste and smells like vinegar.
  • Boiling point is 391 K.
  • When pure CH3COOH is freezed, it forms colorless ice like solid. So it is called glacial acetic acid.

Chemical Properties of Ethanoic Acid

(i) Esterification -Sweet smelling ester is formed. This is saponification as soap is prepared by this.

(ii) Reaction with base: NaOH + CH3COOH → CH3COONa + H2O 

(iii) Reaction with carbonates and hydrogen carbonates : 

2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2 CHH2 

COOH + NaHCOH2 → CH3COONa + H2O + CO2 

SOAPS AND DETERGENTS

  • Soap is sodium or potassium salt of long chain carboxylic acid. Example: C17H35COONa+
  • Soaps are effective only in soft water.
    Detergents are ammonium or sulphonate salt of long chain of carboxylic acid.
  • Detergents are effective in both hard and soft water.
  • Soap molecule has:
    (i) Ionic (hydrophilic) part
    (ii) Long hydrocarbon chain (hydrophobic) part

Cleansing Action of Soap

  • Most dirt is oily in nature and the hydrophobic end attaches itself with dirt and the ionic end is surrounded with molecules of water.
  • This results in formation of a radial structure called micelles.
  • Soap micelles help to dissolve dirt and grease in water and cloth gets cleaned.
  • Soap is a mixture of micelles and helps to dissolve dirt and grease in water and cloth.
  • The magnesium and calcium salt present in hard water react with the soap molecule to form an insoluble product called scum. This scum creates difficulty in cleansing action.
  • By use of detergent, insoluble scum is not formed with hard water and clothes get cleaned effectively.
FORMATION OF MICELLES
  • Elements can be classified as metals and non-metals on the basis of their properties.
  • Examples of some metals are: Iron (Fe), Aluminium (Al), Silver (Ag), Copper (Cu)
  • Examples of some non-metals are: Hydrogen (H), Nitrogen (N), Sulphur (S), Oxygen (O)

PHYSICAL PROPERTIES

CHEMICAL PROPERTIES OF METALS

REACTION OF METALS WITH AIR

  • Metals combine with oxygen to form metal oxide.
  • Metal + O2 → Metal oxide
    Examples:
    (i) 2Cu + O2 → 2CuO Copper oxide (black)                                                        (ii) 4Al + 3O2 → 2Al2O3 Aluminium oxide                                                        (iii) 2Mg + O 2 → 2MgO
  • The reactivity of different metals are different with O2.
  • Na and K react so vigorously that they catch fire if kept in open so they are kept immersed in kerosene.
  • Surfaces of Mg, Al, Zn, Pb are covered with a thin layer of oxide which prevent them from further oxidation.
  • Fe does not burn on heating but iron fillings burn vigorously.
  • Cu does not burn but is coated with black copper oxide.
  • Au and Ag does not react with oxygen.

AMPHOTERIC OXIDES

  • Metal oxides which react with both acids as well as bases to produce salts and water are called amphoteric oxides.
  • Examples:
    (i) Al2O3 + 6HCl → 2AlCl3 + H2O
    (ii) Al2O3 + 2NaOH → 2NaAlO2 + H2O Sodium Aluminate

REACTION OF METALS WITH WATER

  • Metal + Water → Metal oxide + Hydrogen
  • Metal oxide + Water → Metal hydroxide
  • Examples:
    (i) 2Na + 2H2O → 2NaOH + H2 + Heat
    (ii) Ca + 2H2O → Ca(OH)2 + H2
    (iii) Mg + 2H2O → Mg(OH)2 + H2
    (iv) 2Al + 3H2O → Al2O3 + 3H2
    (v) 3Fe + 4H2O → Fe3O4 + 4H2

REACTION OF METALS WITH ACIDS(DILUTE)

  • Metal + Dilute acid → Salt + H2
  • Cu, Ag, Hg do not react with dil. acids.
  • Examples:
    (i) Fe + 2HCl → FeCl2 + H2
    (ii) Mg + 2HCl → MgCl2+ H2
    (iii) Zn + 2HCl → ZnCl2 + H2
    (iv) 2Al + 6HCl → 2AlCl3 + 3H2

REACTION OF METALS WITH SOLUTIONS OF OTHER METAL SALTS

  • Metal A + Salt solution B
  • Salt solution A + Metal B
  • Reactive metals can displace less reactive metals from their compounds in solution form.
  • Fe + CuSO4→ FeSO4 + Cu

REACTIVITY SERIES

The reactivity series is a list of metals arranged in the order of their decreasing activities.

REACTION OF METALS WITH NON-METALS

  • Reactivity of elements is the tendency to attain a completely filled valence shell.
  • Atoms of the metals lose electrons from their valence shell to form cation. Atom of the non-metals gain electrons in the valence shell to form anion.
  • E.g.: Formation of NaCl
    Sodium cation Na → Na+ + e- 2, 8, 1 2, 8
    Chloride anion Cl + e- → Cl- 2, 8, 7 2, 8, 8

IONIC COMPOUNDS

The compounds formed by the transfer of electrons from a metal to a non-metal are called ionic compounds or electrovalent compounds.
FORMATION OF IONIC COMPOUNDS

FORMATION OF IONIC COMPOUNDS

(i) Physical nature: They are solid and hard, generally brittle. 
(ii) Melting and Boiling Point: They have high melting and boiling point. 
(iii) Solubility : Generally soluble in water and insoluble in solvents such as kerosene, petrol etc. 
(iv) Conduction of electricity : Ionic compounds conduct electricity in molten and solution form but not in solid state. 

OCCURENCE OF METALS

(i) Minerals: The elements or compounds which occur naturally in the earth’s crust are called minerals. 
(ii) Ores: Minerals that contain very high percentage of particular metal and the metal can be profitably extracted from it, such minerals are called ores. 

EXTRACTION OF METALS FROM ORES

  • Step 1. Enrichment of ores. 
  • Step 2. Extraction of metals. 
  • Step 3. Refining of metals. 
  • Steps Involved in Extraction of Metals from Ores
    Gangue → Roasting → Calcination → Reduction

IMPORTANT TERMS

(a) Gangue : Ores are usually contaminated with large amount of impurities such as soil, sand etc. called gangue. 
(b) Roasting : The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is called roasting. 
2ZnS + 3O2 →(Heast) 2ZnO + 2SO2 
(c) Calcination : The carbonate ores are changed into oxides by heating strongly in limited air. This process is called calcination. 
ZnCO3 →(Heat) ZnO + CO2 
(d) Reduction : Metal oxides are reduced to corresponding metals by using reducing agent like carbon. 
ZnO + C → Zn + CO 

REFINING OF METALS

  • The most widely used method for refining impure metal is electrolytic refining.
    (i) Anode : Impure copper 
    (ii) Cathode : Strip of pure copper 
    (iii) Electrolyte : Solution of acidified copper sulphate 
  • On passing the current through the electrolyte, the impure metal from anode dissolves into the electrolyte.
  • An equivalent amount of pure metal from the electrolyte is deposited at the cathode.
  • The insoluble impurities settle down at the bottom of the anode and is called anode mud.

CORROSION

  • The surface of some metals get corroded when they are exposed to moist air for a long period of time. This is called corrosion.
  • Examples:                                                                                                                 (i) Silver becomes black when exposed to air as it reacts with air to form a coating of silver sulphide.                                                                       (ii) Copper reacts with moist carbon dioxide in the air and gains a green coat of copper carbonate.                                                                      (iii) Iron when exposed to moist air acquires a coating of a brown flaky substance called rust.

PREVENTION OF CORROSION

  • The rusting of iron can be prevented by painting, oiling, greasing, galvanizing, chrome plating, anodizing or making alloys.
  • Galvanization : It is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
  • Alloy : An alloy is a homogeneous mixture of two or more metals or a metal and a non- metal.
  • Examples of alloy:
    (i) Iron : Mixed with small amount of carbon becomes hard and strong.
    (ii) Steel : Iron + Nickel and chromium
    (iii) Brass : Copper + Zinc
    (iv) Bronze : Copper + Tin (Sn)
    (v) Solder : Lead + tin
    (vi) Amalgam : If one of the metal is mercury (Hg). 
  • The sour and bitter tastes of food are due to acids and bases present in them.
  • Acids are sour in taste and change the color of blue litmus to red.
  • Litmus solution is a purple dye, which is extracted from lichen. When the litmus solution is neither acidic nor basic, its color is purple. 
  • Other natural materials like red cabbage leaves, turmeric, coloured petals of some flowers such as Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a solution. 

PROPERTIES OF ACIDS

  • The term ‘acid’ has been derived from the Latin word, ‘acidus’ which means sour. 
  • Acids have sour taste. 
  • They turn blue litmus solution red.
  • They give H+ ions in aqueous solution.

TYPES OF ACIDS

  • Strong Acids: HCl, H2 SO4 , HNO3
  • Weak Acids: CH3COOH, Oxalic acid, Lactic acid
  • Concentrated Acids: More amount of acid + Less amount of water
  • Dilute Acids: More amount of water + Less amount of acid

PROPERTIES OF BASES

  • These are the substances which are bitter in taste and soapy in touch.
  • They turn red litmus solution blue.
  • They give OH- ions in aqueous solution.

TYPES OF BASES

  • Strong Bases: NaOH, KOH, Ca(OH)2
  • Weak Bases: NH4OH
  • Alkalis: These are bases which are soluble in water. Examples: NaOH, KOH, Ca(OH)2.

TYPES OF INDICATORS AND ITS PROPERTIES

INDICATORS

Substances which change their colour/smell in different types of substances (like acids and bases).

TYPES OF INDICATORS

(i) Natural indicators: Found in nature in plants. Examples: Litmus, red cabbage leaves extract, flowers of hydrangea plant, turmeric. 
(ii) Synthetic indicators: These are chemical substances. Examples: Methyl orange, phenolphthalein. 
(iii) Olfactory indicators: These substances have different odour in acid and bases. 

REACTION OF ACIDS AND BASES WITH METALS

REACTION OF ACIDS WITH METALS

  • Acids react with metal to form metal salt and releases Hydrogen Gas.
    Acid + Metal → Salt + Hydrogen Gas
  • Example: Zinc granules react with dilute Hydrochloric acid in a test tube.
    2HCl + Zn → ZnCl2 + H2

REACTION OF BASES WITH METALS

  • Bases react with metal to evolve hydrogen Gas.
  • The metal must be more reactive than the metals present in the base for the reaction to take place.
    Base + Metal → Salt + Hydrogen gas
  • Example: Zinc granules react with NaOH solution to form sodium zincate and evolve hydrogen gas.
    2NaOH + Zn → Na2ZnO2 + H2
  • Hydrogen gas released can be tested by bringing a burning candle near gas bubbles, it bursts with a pop sound.

REACTION OF ACIDS WITH METAL CARBONATES AND HYDROGENCARBONATES

  • Acids reacts with Metal Carbonates and Metal Hydrogencarbonates to form Salt, Carbon dioxide and water.
  • Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water
  • Examples: (i) 2HCl + Na2CO3 → 2NaCl + CO2 + H2O
    (ii) HCl + NaHCO3 → NaCl + CO2 + H2O
  • CO2 can be tested by passing it through lime water. It turns lime water milky.
  • Ca(OH)2 + CO2 → CaCO3 + H2O
  • When excess CO2 is passed, milkiness disappears.
  • CaCO3 + CO2 + H2O → Ca(HCO)3
  • Bases do not react with Metal Carbonates and Metal Hydrogencarbonates.
  • Base + Metal Carbonate/Metal Hydrogen Carbonate → No Reaction

REACTION OF ACIDS AND BASES WITH EACH OTHER

  • Acids and Bases react to form salt and water.
  • Acid + Base → Salt + H2O

NEUTRALIZATION REACTION

  • Reaction of acid with a base is called a neutralization reaction.
  • Example: HCl + NaOH → NaCl + H2O
  • Strong Acid + Weak Base → Acidic salt + H2O
  • Weak Acid + Strong Base → Basic salt + H2O
  • Strong Acid + Strong Base → Neutral salt + H2O
  • Weak Acid + Weak Base → Neutral salt + H2O

REACTION OF METALLIC OXIDES WITH ACIDS

  • Metallic oxides are basic in nature.
  • Example: CaO, MgO are basic oxides.
  • Metallic Oxide + Acid → Salt + H2O
  • CaO + 2HCl → CaCl2 + H2O

REACTION OF NON-METALLIC OXIDES WITH BASES

  • Non-metallic oxides are acidic in nature.
  • Non-metallic Oxide + Base → Salt + H2O
  • CO2 + Ca(OH)2 → CaCO3 + H2O

REACTION OF ACID

(i) Acid + Metal Carbonate → Salt + CO2 + Water 
(ii) Acid + Metal → Salt + H2 
(iii) Acid + Metal Hydrogen Carbonate → Salt + CO2 + H2O 
(iv) Acid + Metallic oxide → Salt +H2O 
(v) Acid + Base → Salt + H2O 

REACTION OF BASE

(i) Base + Metal → Salt + H2 
(ii) Base + Metal Carbonate → No Reaction 
(iii) Base + Metal Hydrogen Carbonate → No Reaction 
(iv) Base + Acid → Salt + H2O 
(v) Base + Non Metallic oxide → Salt + H2O 

SIMILARITIES BETWEEN ALL ACIDS AND ALL BASES

  • All acids have H+ ions in common. All acids produce H+ ions
  • Acids produce H+ ions in solution which are responsible for their acidic properties.
  • All bases have OH- (hydroxyl ions) in common. All bases produce OH- ions

ACID OR BASE IN WATER SOLUTION

  • Acids produce H+ ions in the presence of water.
  • H+ ions cannot exist alone, they exist as H3O+ (hydronium ions).
  • H+ + H2O → H3O+
  • HCl + H2O → H3O+ + Cl-
  • Bases when dissolved in water give OH − ions.
  • Bases soluble in water are called alkali.
  • While diluting acids, it is recommended that the acid
    should be added to water and not water to acid because
    the process of dissolving an acid or a base in water is highly exothermic.

STRENGTH OF ACID AND BASE SOLUTIONS

  • Strength of acid or base can be estimated using a universal indicator.
  • Universal indicator: It is a mixture of several indicators. It shows different colours at different concentrations of H+ ions in the solution.
  • pH Scale: A scale for measuring H+ ion concentration in a solution. p in pH stands for ‘potenz’ a German word which means power.
  • If value of ph is equal to 7 → neutral solution
  • If value of pH is less than 7 → acidic solution
  • If value of pH more than 7 → basic solution
  • Most of the substance around us undergoes various changes. Some of these changes are temporary with no new substance being formed. They are called physical changes.
  • In certain other changes the new substance formed in which the reactant or the parent loses its identity to form new substance called product. These changes are permanent changes as we won’t get the reactant back. 

CHEMICAL REACTION

  • Chemical reaction is the process by which two or more substance react with each other to form new substance with different properties.
  • These are the following changes to determine that the chemical reaction has taken place:
    (i) Change in state 
    (ii) Change in colour 
    (iii) Evolution of gas 
    (iv) Change in temperature 

CHEMICAL EQUATION

  • A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formulae, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side.
  • Magnesium + oxygen → magnesium oxide (Reactant) (Product)

BALANCED CHEMICAL EQUATION

  • The chemical equation that shows the chemical reaction needs to be balanced.
  • A balanced chemical equation occurs when the number of the atoms involved in the reactants side is equal to the number of atoms in the products side.
  • Zn + H2SO4 → ZnSO4 + H2
  • 3Fe (s) + 4H2O(g) → Fe3O4 (s) + 4H2 (g)

TYPES OF CHEMICAL REACTION

1. COMBINATION REACTION:

  • Such a reaction in which a single product is formed from two or more reactants is known as a combination reaction.
    CaO (s) + H2O (l) → Ca(OH)2 (aq)
  • Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat. A solution of slaked lime produced by the reaction is used for white washing walls.
  • Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls. It is interesting to note that the chemical formula for marble is also CaCO3.
    Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)
    (slaked lime) (calcium carbonate)
    Burning of coal: C (s) + O2 (g) → CO2 (aq)
    Formation of water: H2 (g) + O2 (g) → H2O (aq)
    Burning of natural gas (Methane):
    CH4 (g) + O2 (g) → CO2 (g) + H2O (l)

2. EXOTHERMIC REACTION:

  • An exothermic process releases heat, and causes the temperature of the immediate surroundings to rise.
  • The rice, potatoes and bread we eat contain carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy.
  • The special name of this reaction is respiration is an exothermic reaction.
    C6H12O6 (aq) + 6O2 (aq) → 6CO2 + 6H2O (l) + energy (glucose)

3. ENDOTHERMIC REACTION:

  • An endothermic process absorbs heat and cools the surroundings.
  • The decomposition of vegetable matter into compost is also an example of an endothermic reaction.

4. DECOMPOSITION REACTION:

  • When single reactant breaks down to give simpler products. This is a decomposition reaction.
  • White silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine by light.
  • The above reactions are used in black and white photography.

5. DISPLACEMENT REACTION:

  • Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound.
  • Both metals and non-metals take part in displacement reactions.
  • Reaction of iron nails with copper sulphate solution.
    Fe (s) + CuSO4 (aq) → FeSO4 (g) + Cu (s)
    Pb (s) + CuCl2 (aq) → PbCl2 (aq) + Cu (s)

6. DOUBLE DISPLACEMENT REACTION:

  • A double displacement reaction, also known as a double
    replacement reaction or metathesis, is a type of chemical reaction where two compounds react, and the positive ions (cation) and the negative ions (anion) of the two reactants switch places, forming two new compounds or products.
  • Na2(SO)4 (aq) + BaCl2 (aq) → BaSO4 (s) + NaCl (aq)

7. REDOX REACTION:

  • An oxidation-reduction (Redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species. An oxidation-reduction reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron.

  • Oxidation: This process involves gain of oxygen or loss of hydrogen.

  • Reduction: This process involves gain of hydrogen or loss of oxygen. 

  • Oxidizing Agent: It is the substance which gives oxygen or gains hydrogen. Or it is the substance which is reduced itself and oxidizes other. 

  • Reducing Agent: It is the substance which gives hydrogen or gains oxygen. Or it the substance which is oxidized itself and reduces other.
    Oxidation is the process which involves loss of electrons but reduction is the process which involves gain of electrons. 

     

CORROSION

The process of slow conversion of metals into their undesirable compounds due to their reaction with oxygen, water, acids, gases etc. present in the atmosphere is called corrosion.

RUSTING

Iron when reacts with oxygen and moisture forms red substance called rust.

RANCIDITY

  • The taste and odour of food materials containing fat and oil changes when they are left exposed to air for long time. This is called rancidity. It is caused due to oxidation of fat and oil present in food material. 
  • It can be prevented by using various methods such as by adding antioxidants to the food materials, storing food in air tight container and by flushing out air with nitrogen. 
  • All living organisms need food for health, growth and development.
  • Food provides nutrients like carbohydrates, fats, protein, vitamins and minerals.
  • Both plants and animals are major sources of food.
  • India has a high population of more than one billion and is still growing.
  • To feed this growing population we need more than a quarter of a billion tonnes of grain per year.
  • This can be done by farming on more land but India is already intensively cultivated. Hence, it is necessary to increase the efficiency of production for both crops and livestock.

GREEN REVOLUTION

Green revolution is a programme introduced in many countries to increase food production by use of modern technology, proper irrigation, improved seeds etc.

WHITE REVOLUTION

White revolution is a programme in India to increase production of milk in India. This programme made India self-sufficient in production of milk.

IMPROVEMENTS IN CROP YIELDS

Types of Crops:
(i) Cereals: They include crops like wheat, rice, maize, barley etc. They provide us carbohydrates.
(ii) Seeds: Not all seeds of plants are edible like seeds of apple or cherries. Edible seeds include cereals, pulses, oil seeds and nuts. They provide us fats.
(iii) Pulses: They include legumes such as gram, pea, black gram, green gram, lentil. They provide us proteins.
(iv) Vegetables, spices and fruits: They provide us vitamins & minerals. They include apple, mango, cherry, banana, water-melon etc. Vegetables like spinach, leafy vegetables, carrot etc. Spices like chilly, black pepper, fodder crops, oats etc.

CROP SEASON

Different crops require different conditions (temperature, moisture, etc.), different photo-periods (duration of sunlight) for their growth and completing life cycle.

THE TWO TYPES OF CROPS SEASON ARE:

(i) Kharif Season: These crops grow during rainy season (June to October). Example: black gram, green gram, pigeon pea, rice, paddy, soyabean.
(ii) Rabi Season: These crops are grown during November to April. Rabi crops are known as winter crops. Example: wheat, gram, peas, mustard, linseed etc.

APPROACHES WHICH ENHANCE THE CROP YEILD ARE AS FOLLOWING:

(i) Crop variety improvement 
(ii) Crop production improvement 
(iii) Crop protection improvement 

(i) CROP VARIETY IMPROVEMENT

Factors by which variety improvement can be done are:
(i)Good and healthy seeds
(ii)Hybridization: It is the process of crossing between two or more genetically dissimilar plants to produce a new variety with good properties of both the crops.

Properties to be possessed by improved seeds:

(i) Higher yield: To increase the productivity of the crop per acre. 
(ii) Improved quality: Quality of crop products vary from crop to crop. 
(iii) Biotic & Abiotic resistances : Crop production reduces due to biotic and abiotic factors. Varieties resistant to these factors can improve crop production. 
(iv) Wider adaptability : Crops which can grow in different conditions, will help in setting high production. 
(v) Desired agronomic traits: Crops which contain desired agronomic traits (height, branching, leafs), sets high production. 

(ii) CROP PRODUCTION IMPROVEMENT

  • It involves different practices carried out by farmers to achieve higher standards of crop production.
  • The different practices are:
    (a)Nutrient management
    (b)Irrigation
    (c)Cropping patterns

(a) Nutrient Management

Like other organisms, plants also require some elements for their growth. These elements are called nutrients.
Manure:
  • To increase the yield, the soil can be enriched by supplying nutrients in the form of manure and fertilizers.
  • Manure is a source of organic matter.
  • It supplies small quantities of nutrient to the soil.
  • It is prepared by the decomposition of animal excreta and plant waste.
Various forms of Manures :

(i)Compost: The process in which animal excreta (like cow dung), kitchen waste, plant remains, waste food, sewage waste etc. are decomposed in pits is known as composting.

(ii)Vermicompost: Compost prepared by using earthworms to hasten the process of decomposition of plants and animals refuse is called vermicompost.

(iii)Green manure: Some plants like sun hemp, guar etc. are grown and after sometime mulched by ploughing in the field. These green plants turn into green manures. They are rich in nitrogen and phosphorus.

Fertilizers
  • Fertilizers are prepared in factories. They are made up of chemical substances.
  • They have large amount of nutrients like nitrogen, phosphorus and potassium.
  • Fertilizers are easily absorbed by the plants since they are soluble in water. It is costly.
Difference between Manures and Fertilizers

(b) Irrigation

The process of supplying water to the crop plants is called irrigation.
Methods of Irrigation :

(i) Two types of wells: 
• Dug wells: In dug wells, water is collected by bullock-operated devices or by pumps. 
• Tube wells: It makes very deep underground water available for irrigation. Motor pump is used to lift water. 
(ii) Canals: These get water from large rivers. 
(iii) River lift system: In this system, water is directly taken from rivers through pumps. This system is useful for irrigation in areas close to river. 
(iv) Tanks: These are small storage reservoirs. 
(v) Rain water harvesting: Rain water harvesting is a accumulation of water in tanks for later use. This also prevents soil erosion.  

(c) Crop Patterns

  • Different patterns are used to maximize the production from crop field.
  • The different patterns are:
    (i) Mixed cropping: Growing two or more than two crops together on the same piece of land is called mixed cropping.
    Examples: wheat and gram, wheat and mustard, groundnut and sunflower.
    (ii) Inter cropping: Two or more crops are grown on the same field in a definite pattern. Few rows of one followed by few rows of the other.
    Examples: Soyabean+maize, Finger nullet (Bajra)+Cow pea (lobia)
    (iii) Crop rotation: Crop rotation is policy of growing different crops one after another on the same field. If some crop is grown again and again on the same field, same nutrients are extracted from soil again and again. So we should choose different crops so that all nutrients of soil are used. 
Advantages of crop rotation:

(i) Soil fertility is maintained. 
(ii) It controls pests and weeds. 
(iii) Several crops can be grown in succession with only one soil preparation. 

(iii) CROP PROTECTION IMPROVEMENT

To protect crops against diseases caused by organisms and other harming factors is called crop protection.

Methods used to control the problems:

I. Pest control during growth- Pest is any destructive organism which can destroy or harm crops or products obtained from them. Types of pests:
(i) Weeds: Unwanted plants in the cultivated field. Example: xanthium.
(ii) Insects: Insects can harm plants in the following ways : they cut the root, stem and leaf, they suck the cell sap from various parts of the plant.
(iii) Pathogens: Any organism such as bacteria, fungi and viruses which cause diseases in plants are called pathogens. They are transmitted through air, water, and soil.
II. Storage of grains-For getting seasonal foods throughout the year, they are stored in safe storage. But during storage of grains, they can be destroyed and wasted by various means.
(i) Biotic problem: Due to living organisms like insects, birds, mites, bacteria, fungi. 
(ii) Abiotic problem: Due to non-living factors such as moisture, inappropriate temperature etc. These factors affect quality degradation, loss in weight, change in color, poor germinability. 

ORGANIC FARMING

  • Use of fertilizers and pesticides has their own disadvantages. They cause pollution, damage soil fertility in the long run. Grains, fruits, and vegetables obtained may contain harmful chemicals in small amounts.
  • Organic farming is a farming system with no or very little use of chemicals like fertilizers and pesticides.

Ways to protect food grains before they are stored for future use:

(i) Drying: The food grains should be properly dried in the sun. 
(ii) Maintenance of hygiene: The grains must not contain insects. The godowns should be cleaned well. The cracks in the roof and on the walls and floor should be sealed completely. 
(iii) Fumigation: Godowns and stores should be properly sprayed with fumigants. Specially, the seeds should be treated with insecticides and fungicides. 
(iv) Storage devices: Cleaned and dried grains should be stored in gunny bags or other proper bags. Airtight, moisture-resistant and temperature resistant storage devices have been developed by various organizations.

ANIMAL HUSBANDRY

Animal husbandry is a scientific management of domestic animals in an efficient manner to obtain food and other useful products from them.

Purpose of cattle farming:

(i) For getting milk 
(ii) Plowing fields 
(iii) Bull cart for transportation 

Types of cattle:

  • Cow (Bos indicus)
  • Buffalo (Bos bubalis)
  • Milch animals: These include milk producing animals (female cattle).
  • Draught animals: Those animals which do not produce milk and are used for agricultural work.
  • Lactation period: The period of milk production between birth of a young one and the next pregnancy is called lactation period.

Care of cattle:

(i) Cleanliness:
→ Roofed shelter with good ventilation for protection from rain, heat and cold.
→ Regular brushing of cattle skin.
→ Sloping floor for shelter to avoid water-logging.
(ii) Food:
→ Roughage mainly containing fiber
→ Concentrates containing proteins
→ Food containing micro nutrients (vitamins and minerals) for enhanced milk production.
(iii) Diseases: Diseases can cause death and reduce milk production.
→ Parasites are small organisms living inside or outside the body of another organism (host). They derive food from the body of the host.
→ External parasites on the skin of cattle cause skin diseases.
→ Internal parasites like worms cause stomach and intestine problems and flukes cause liver problems.
→ Bacteria, virus cause infectious diseases (diseases that can be easily transmitted from one to another).
(iv) Poultry Farming: Poultry farming is done for eggs and meat. They both provide protein to our diet. 
(v) Broilers: Birds grown for obtaining meat are called broilers. They can be used after 6-8 weeks from their birth. 
(vi) Layers: Birds grown for obtaining eggs are called layers. They can be used after 20 weeks when sexual maturity has been attempt to lay eggs.
→ Most of the broilers and layers are cross-breed.
→ Breeding is done to enhance following properties in hens like:
More and better quality chicks, low maintenance, breeding is done to produce dwarf broilers (meat-giving birds). Feeding cost is the biggest expense in poultry farms. 
→ Dwarf broilers need less food and can reduce cost by 30%. Also, they can tolerate more heat. 

FISH PRODUCTION

Fish production is a great source of protein in our diet.

Types of Fish Production:

(i) Finned fish production/True fish production: Production and management of cartilaginous and bony fishes such as pomfret, tuna, catla, prawns, rohu etc.  
(ii) Unfinned fish production: Production of shellfish such as prawns, molluscs.  

Types of Obtaining Fishes:

(i) Capture fishing: Naturally living fishes in various water bodies are captured.
(ii) Culture fishing: Fishes of desired variety are cultivated in confined areas with utmost care to get maximum yield. This is also called aquaculture. Aquaculture can be done in oceans, rivers, lakes, ponds etc. When it is done in oceans, it is called mariculture.                                                                                (a)Marine fishing: Marine fishing includes fish production in ponds, rivers, and reservoirs. Popular marine fishes include pomfret, tuna, sardines, Bombay duck. Some costly fishes found in the sea like mullets, prawns, seaweed, oysters. Using satellites, regions of high fish population in the sea can be found. Echo-sounders are also used.
(b)Inland fishing: It includes fish production in freshwater (for example ponds, rivers, lakes, reservoirs) and brackish water (for example estuaries). 

Composite Fish Culture:

  • 5 to 6 varieties in a single fish pond. 
  • They are selected so that they do not compete for food. They should have different food requirements. 

  • Example of Fish: Catla: Feeds in the upper part of water, Rohu: Feeds in the middle part of water, Marigals, common carps: Feeds at the bottom. 

Advantage of Fishing:

More yield.

Problems of Fishing:

Many fishes lay eggs during monsoons only, due to which many fishes will not grow fast. So hormonal stimulation is used. Using this, fishes can be made to reproduce at any time. 

BEE-KEEPING

  • It is the practice of keeping, caring & managing honeybees on a large scale for obtaining honey and wax.
  • Many farmers use bee-keeping for an additional small income. Also, there are big farms called apiaries/bee farms.

Apiary:

  • The setting up of some beehives in a desirable location in a systematic manner that allows maximum pollen and nectar collection.
  • Some common Indian varieties of bees include Apis cerana indica (Indian bee), dorsata (rock bee), floral (little bee).
  • One Italian variety mellifera is also used in India for commercial large scale production.

Advantages of Italian variety Mellifera:

(i) High honey collection capacity. 
(ii) They reproduce fast. 
(iii) They are stingless. 
(iv) They stay in a beehive for a long time. 

Honey:

  • It is a dense sweet liquid. 
  • It is used in medicines. It is used as sugar. 
  • It is used as a source of energy. 

Pasturage :

  • Pasturage is the availability of flowers to the bees for nectar and pollen collection. 
  • Pasturage of flora is the type of crop, flower or other plants from which bees collects nectar and pollen to produce honey. 
  • It affects the quality and quantity of honey because different flora produces nectar and pollen of different types such as almond honey of Kashmir is very tasty. 
  • ‘Health’ is a state of being well enough to function well physically, mentally and socially.
  • Disease: Any disturbance in the structure or function of any organ or part of body.
  • The various causes of diseases are pathogens (virus, bacteria), lack of nutritious diet/balanced diet and lack of public health services.
  • Acute diseases occur suddenly and lasts for a short duration while chronic diseases develop slowly and lasts for long period of time.
  • The diseases/infections can be prevented by life style (exercise, proper sleep, enough relaxation) modification, taking balanced diet, good personal health and hygiene and also maintaining a clean and healthy surrounding.
  • Treatment involves killing of the microbes/pathogens.

HEALTH

  • Health is a state of physical, mental and social well-being. The conditions necessary for good health are:
    (i) Good physical and social environment.
    (ii) Good economic conditions.
  • Good physical and social environment includes clean surroundings, good sanitation, proper garbage disposal and clean drinking water.
  • Good economic conditions includes job opportunities for earning to have nutritious food and to lead a healthy life.
  • Personal and Community Issues Both Matter for Health

COMMUNITY HEALTH

  • All those activities which people do both individually and in groups for the development of their society, constitute the community health.
  • Personal and community health are supplementary to each other.
  • We protect ourselves by keeping our body clean.
  • For this, we also require a good and healthy environment in our surroundings.
  • We can have this only by the means of community health and development.
  • So, both personal and community health are inter-related.

DIFFERENCES BETWEEN BEING HEALTHY AND DISEASE-FREE

DISEASE AND ITS CAUSES

What does disease look like?
(i)When a person is affected by a disease either the functioning or the appearance of one or more systems of the body will change for the worse.
(ii)These changes give rise to symptoms and signs of disease.
(iii)On the basis of the symptoms the physicians look for the signs of a particular disease and conduct tests to confirm the disease.

Types of Diseases

  • Acute Diseases: Acute diseases which last for only very short period of time and affect body suddenly and quickly. Example: Cold, cough, typhoid etc.
  • Chronic Diseases: The diseases which last for a long time, even as much as a life time, are called chronic diseases. Example: Diabetes, tuberculosis, elephantiasis etc.

Causes of Diseases

Diseases are caused by:
→ Pathogens like virus, bacteria, fungi, protozoans or worms. 
→ Poor health and under nourishment. 
→ Hereditary and genetic disorder. 
→ Lack of proper treatment of immunization. 
→ Environmental pollution (air, water etc.) 

Infectious and Non-infectious Diseases

(i) Infectious Diseases: The diseases which spread due to infection by micro- organisms are called infectious diseases. It is communicated from diseased person to healthy person, caused by some biological agents/pathogens like viruses, bacteria, fungi, protozoans, fungi worms. 
(ii) Non-infectious Diseases: The disease which does not spread by contact between infected and healthy person through air and water, is called non-infectious disease. Example: Arthritis, heart disease.

(i)SARS Viruses

  • SARS viruses are coming out of the surface of an
    infected cell (see the arrows for example).
  • 500 nanometer = 0.5 micrometer = 0.001 millimeter.

(ii)Trypanosoma

  • Trypanosoma is a protozoan organism.
  • It causes sleeping sickness.
  • The saucer-shaped substance lying next to the protozoa, is a red blood cell.

(iii)Staphylococcus bacteria

  • The Staphylococcus bacteria causes acne.
  • The scale is indicated at the line at the top left of the picture. It is 5 micrometers long.

(iv)Adult roundworm

  • Adult roundworm is found in the small intestine.
  • Its technical name is Ascaris Lumbricoides.
  • The ruler next to it shows 4 centimeter to give an idea of the scale.

(v)Leishmania

  • Leishmania, the protozoan organism causes kala-azar.
  • The organisms are oval-shaped, and each has one long whip-like structure.
  • The immune cell is about ten micrometres in diameter.

(vi)Microorganisms

(vii)Antibiotics

  • Antibiotics blocks biochemical pathways important for bacteria. Hence, they are effective against them. Example:Penicillin, tetracycline.
  • Many bacteria make a cell wall to protect themselves, the antibiotics (Penicillin) blocks the bacterial process that builds cell wall.
  • Antibiotics works only against the bacteria and not against the viruses.

Means of Spread of Infectious Diseases

  • Infectious diseases spread from an infected person to a healthy person through air, water, food, vectors, physical contact and sexual
    contact.
  • Through air: By sneezing and coughing, the microbes spread into air and enter into the body of a healthy person, like common cold, tuberculosis, pneumonia etc.
  • Through water : The microbes enter into our body by drinking/eating polluted and contaminated water/food, like cholera, amoebic dysentery etc.
  • Vectors: Some organisms like female anopheles mosquito also work as a vector of disease, like malaria, dengue, yellow fever etc.
  • Through sexual contact: Syphilus, AIDS spread by sexual contact with infected person. AIDS virus can also spread through blood transfusion and from the mother to her child during pregnancy and through breast feeding.

AIDS(Acquired Immuno Deficiency Syndrome)

AIDS is caused by a retro-virus called HIV (Human Immuno Deficiency Virus).
Method of transmission of AIDS

The transmission of AIDS from an infected to a healthy person takes place :

  • Through sexual contact
  • Blood transfusion
  • Use of infected needle or blade etc.
  • This may also get transmitted from infected
    mother to her foetus.
Prevention of AIDS
  • Avoid transfusion of infected blood. This can be done by testing whether the blood is HIV negative or not.
  • Always use disposable needle and syringe.
  • Avoid sexual contact with unknown person.
  • Avoid the same razor used in the salons.

ORGAN – Specific and Tissue-specific Manifestations

  • Disease causing microbes enter the body by different means and goes to different organs and tissues.
  • Microbes which enter through the nose are likely to go to the lungs. (Bacteria which cause tuberculosis of lungs).
  • Microbes which enter through the mouth are likely to stay in the gut (bacteria which causes typhoid) or liver (bacteria which causes jaundice).
  • Virus which causes AIDS enter the body through sexual organs during sexual contact and spread through the lymph to all parts of the body and damages the immune system.
  • Virus which causes Japanese encephalitis (brain fever) enters the body through mosquito bite and goes and infects the brain.

PRINCIPLES OF TREATMENT

The treatment of infectious diseases consists of two steps. They are to reduce the effects of the disease (symptoms) and to kill the microbes which caused disease.

(i) To reduce the effects of the disease: This can be done by taking medicines to bring down the effects of the disease like fever, pain or loose motions etc. and by taking bed rest to conserve our energy.

(ii) To kill the microbes: This can be done by taking suitable antibiotics and drugs which kills the microbes and the disease is cured.

PRINCIPLES OF PREVENTION

  • There are two ways of prevention of infectious diseases. They are general ways and specific ways.                                                                       (i) General ways of prevention: Public hygiene is most important for prevention of infectious diseases. Proper and sufficient food for everyone will make people healthy to resist the infection.
  • Air borne diseases can be prevented by living in conditions that are not crowded. Water borne diseases can be prevented by providing safe drinking water.
  • Vector borne diseases can be prevented by providing clean environment.                                                                                                          (ii) Specific ways of prevention: There are disease specific measures which are used to fight them. It is done by Immunisation.
  • This is the process of introducing a weakened pathogen inside the body of the host to fool his/her immune system to produce antibodies against that particular disease.
  • Not only does our immune system fight the disease (feeble pathogen), but also keeps a memory of the incident by keeping those antibodies in blood.
  • Thus, next time even if the disease will strike the host’s body with full vigour, the body will be able to protect itself with the help of these antibodies.This is also the basic law followed by vaccination programmes done for infants.
  • The sensation felt by our ears is called sound.
  • Sound is a form of energy which makes us hear.
  • Law of conservation of energy is also applicable to sound.
  • Sound travels in form of wave.

PRODUCTION OF SOUND

  • Sound is produced when object vibrates or sound is produced by vibrating objects.
  • The energy required to make an object vibrate and produce sound is provided by some outside source (like our hand, wind etc.).
  • Example: Sound of our voice is produced by vibration of two vocal cords in our throat.
  • Sound of a drum or tabla is produced by vibration of its membrane
    when struck.
  • In laboratory experiments, sound is produced by vibrating tuning fork. 
  • The vibrations of tuning fork can be shown by touching a small suspended pith ball (cork ball) with a prong of the sounding tuning fork. The pith ball is pushed away with a great force. 

Sound can be produced by following methods:

  • By vibrating string (sitar) 
  • By vibrating air (flute) 
  • By vibrating membrane (table, drum) 
  • By vibrating plates (bicycle bell) 
  • By friction in objects 
  • By scratching or scrubbing the objects etc. 

PROPAGATION OF SOUND

  • The substance through which sound travels is called a medium.
  • The medium may be solid, liquid or gas.
  • When an object vibrates, then the air particles around it also start vibrating in exactly the same way and are displaced from their stable position.
  • These vibrating air particles exert a force on nearby air particles so they are also displaced from
    their rest position and start to vibrate.
  • This process is continued in the medium till sound reaches our ears.
  • The disturbance produced by sound travels through the medium (not the particles of the medium).
  • Wave is a disturbance which travels through a medium and carries energy.
  • So sound travels in wave form known as mechanical waves.
  • When a body vibrates then it compresses the air surrounding it and form a area of high density called compression (C).
  • Compression is the part of wave in which particles of the medium are closer to one another forming high pressure.
  • This compression move away from the vibrating body.
  • When vibrating body vibrates back a area of low pressure is formed called rarefaction (R).
  • Rarefaction is the area of wave in which particles of the medium are further apart from one another forming a low pressure or low density area.
  • When body vibrates back and forth, a series of compression and rarefaction is formed in air resulting in sound wave.
  • Propogation of sound wave is propogation of density change.

Sound needs Medium for Propagation:

  • Sound waves are mechanical waves.
  • It needs material medium for propogation like air, water, steel etc.
  • It cannot travel in vaccum.
  • An electric bell is suspended in airtight bell jar connected with vacuum pump.
  • When bell jar is full of air, we hear the sound but when air is pumped out from the bell jar by vacuum pump and we ring the bell, no sound is heard.
  • So, medium is necessary for propagation of sound. Experiment to show that sound cannot travel through vacuum

SOUND WAVES AS LONGITUDINAL WAVES

  • A wave in which the particles of the medium vibrate back and forth in the same direction in which the wave is moving, is called a longitudinal wave.
  • When we push and pull the slinky compression (number of turns are more or closer) and rarefaction (number of. turns are less or farther) are formed.
  • When a wave travels along with slinky, its each turn moves back and forth by only a small distance in the direction of wave. So the wave is longitudinal.
  • The direction of vibrations of the particles is parallel to the direction of wave.
  • When one end of a slinky is moved up and down rapidly whose other end is fixed, it produces transverse wave.
  • This wave possess along the slinky in horizontal direction, while turns of slinky (particles) vibrate up and down at right angle to the direction of wave.
  • Thus in transverse wave particles of the medium vibrate up and down at right angles to the direction of wave.
  • Light waves are transverse waves but they don’t need a material medium for propagation. 

CHARACTERISTICS OF SOUND WAVES

  • The characteristics of sound waves are : wavelength, frequency, amplitude, time period and velocity.
  • When a wave travel in air the density and pressure of air changes from their mean position.
  • Compression is shown by crest while rarefaction is shown by trough.
  • Compression is the region of maximum density or pressure.
  • Rarefaction is the region of minimum density or pressure.

WAVELENGTH

  • In sound waves the combined length of a compression and an adjacent rarefaction is called its wavelength.
  • The distance between the centres of two consecutive compressions or two consecutive rarefactions is also called its wavelength.
  • It is denoted by the Greek letter lamda (λ). Its SI unit is metre.

FREQUENCY

  • No. of complete waves produced in one second or number of vibrations per second is called frequency.
  • Number of compressions or rarefactions passed in one second is also frequency.
  • Frequency of wave is same as the frequency of the vibrating body which produces the wave.
  • The SI unit of frequency is hertz (Hz). The symbol of frequency is v (nu).
  • 1 Hertz: One Hz is equal to 1 vibration per second.
  • Bigger unit of frequency is kilohertz kHz = 1000 Hz.

TIME PERIOD

  • Time taken to complete one vibration is called time period.
  • Time required to pass two consecutive compressions or rarefactions through a point is called time period.
  • SI unit of time period is second (s). Time period is denoted by T.
  • The frequency of a wave is the reciprocal of the time period.
  • v = 1/T

AMPLITUDE

  • The maximum displacement of the particle of the medium from their original undisturbed position is called amplitude of the wave.
  • Amplitude is denoted by A and its SI unit is metre (m).
  • Sound have characteristics like pitch and loudness and timbre.

PITCH

  • The pitch of sound depends on the frequency of sound (vibration).
  • It is directly proportional to its frequency. Greater the frequency, higher is the pitch and lesser the frequency, lower is the pitch.
  • A woman’s voice is shrill having a high pitch while a man’s voice is flat having low pitch.
  • High pitch sound has large number of compressions and rarefactions passing a fixed point per unit time.

LOUDNESS

  • The loudness depends on the amplitude of the sound wave.
  • Loudness is the measure of the sound energy reaching the ear per sec.
  • Greater the amplitude of sound wave, greater is the energy, louder the sound; short is the amplitude, less is the energy, soft is the sound.
  • Loudness is measured in decibel ‘dB’.

QUALITY OR TIMBRE

  • The timbre of a sound depends on the shape of sound wave produced by it. It is the characteristic of musical sound.
  • It helps us to distinguish between two sounds of same pitch & loudness.
    Sound of single (same) frequency is called tone while a mixture of different frequencies is called note.
  • Noise is unpleasant to hear while music is pleasant to hear and it is of good quality.

VELOCITY

  • The distance travelled by a wave in one second is called velocity of the wave.
  • Its SI unit is metre per second (ms-1). Velocity = Distance travelled/Time taken                                                                                                                          
  • v = λ/T (λ is the wavelength of the waves travelled in one time time period T)
  • v = λv (1/T = v) So, Velocity = Wavelength × Frequency. This is the wave equation.

SPEED OF SOUND IN VARIOUS MEDIUMS

  • Speed of sound depends on the nature of material through which it travels. It is slowest in gases, faster in liquids and fastest in solids.
  • Speed of sound increases with the rise in temperature.
  • Speed of sound increases as humidity of air increases.
  • Speed of light is faster than speed of sound.
  • In air, speed of sound is 344 ms-1 at 22oC.

SONIC BOOM

  • Some aircrafts, bullets, rockets etc. have ‘supersonic speed’.
  • Supersonic refers to the speed of an object which is greater than the speed of sound and it produces extremely loud sound waves called ‘shock waves’ in air.
  • Sonic boom is an explosive noise caused by shock waves.
  • It emits tremendous sound energy which can shatter the glass panes of windows.

REFLECTION OF SOUND

  • Like light, sound also bounce back when it falls on a hard surface. It is called reflection of sound.
  • The laws of reflection of light are obeyed during reflection of sound.
    (i) The incident sound wave, the reflected sound wave and normal at the point of incidence lie in the same plane.
    (ii) Angle of reflection of sound is always equal to the angle of incidence of sound.

ECHO

  • The repetition of sound caused by the reflection of sound waves is called an echo.
  • We can hear echo when there is a time gap of 0.1 second in original sound and echo (reflected sound).
  • Echo is produced when sound reflected from a hard surface (i.e. brick wall, mountain etc.) as soft surface tends to absorb sound.

Minimum distance to hear an echo:

Rolling of thunder is due to multiple reflection of sound of thunder from a number of reflecting surfaces such as clouds and the earth.

Reverberation:

  • The persistence of sound in a big hall due to repeated reflection of sound from the walls, ceiling and floor of the hall is called reverberation.
  • If reverberation is too long, sound becomes blurred, distorted and confusing due to overlapping of different sound.

Methods to reduce reverberation in big halls or auditoriums:

  • Panels made of felt or compressed fibre board are put on walls and ceiling to absorb sound.
  • Heavy curtains are put on doors and windows.
  • Carpets are put on the floor.
  • Seats are made of material having sound absorbing properties.

APPLICATIONS OF REFLECTION OF SOUND

(i) Megaphone, loudspeakers, bulb horns and trumpets, shehnai etc. are designed to send sound in a particular direction without spreading all around. All these instruments have funnel tube which reflects sound waves repeatedly towards audience. In this amplitude of sound waves adds up to increase loudness of sound. 

(ii) Stethoscope: It is a medical instrument used for listening the sounds produced in human body mainly in heart and lungs. The sound of the heartbeats reaches the doctor’s ears by the multiple reflection of the sound waves in the rubber tube of stethoscope. 
(iii) Sound Board: In big halls or auditoriums sound is absorbed by walls, ceiling, seats etc. So a curved board (sound board) is placed behind the speakers so that his speech can be heard easily by audiences. The soundboard works on the multiple reflection of sound.  
(iv) The ceiling of concert halls are made curved, so that sound after reflection from ceiling, reaches all the parts of the hall.  

RANGE OF HEARING

  • Range of hearing in human is 20 Hz to 20000 Hz. Children younger than 5 years and dogs can hear upto 25 KHz. The sounds of frequencies lower than 20 Hz are known as ‘infrasonic sounds’.
  • A vibrating simple pendulum produces infrasonic sounds.
  • Rhinoceroses communicate each other using frequencies as low as 5 Hz.
  • Elephants and whales produces infrasonic waves.
  • Earthquakes produces infrasonic waves (before shock waves) which some animals can hear and get disturbed.
  • The sounds of frequencies higher than 20 KHz are known as ‘ultrasonic waves’.
  • Dogs, parpoises, dolphins, bats and rats can hear ultrasonic sounds.
  • Bats and rats can produce ultrasonic sounds.

HEARING AID

  • It is battery operated electronic device used by persons who are hard of hearing.
  • Microphone convert sound into electrical signals, than those are amplified by amplifier. Amplified signals are send to the speaker of hearing aid. The speaker converts the amplified signal to sound and sends to ear for clear hearing.

APPLICATIONS OF ULTRASOUND

(i) It is used to detect cracks in metal blocks in industries without damaging them. 
(ii) It is used in industries to clean ‘hard to reach’ parts of objects such as spiral tubes, odd shaped machines etc. 
(iii) It is used to investigate the internal organs of human body such as liver, gall bladder, kidneys, uterus and heart. 
(iv) Ecocardiography: These waves are used to reflect the action of heart and its images are formed. This technique is called echocardiography. 
(v) Ultrasonography: The technique of obtaining pictures of internal organs of the body by using echoes of ultrasound waves is called ultrasonography. 
(vi) Ultrasound is used to split tiny stones in kidneys into fine grains. 

SONAR

  • The word ‘SONAR’ stands for ‘Sound Navigation And Ranging’.
  • SONAR is a device which is used to find distance, direction and speed of underwater objects.
  • SONAR consists of a transmitter and a receptor or detector and installed at the bottom of a ship.
  • The transmitter produces and transmits ultrasonic waves.
  • These waves travel through water and after striking the objects on the bottom of sea, are reflected back and received by detector.
  • These reflected waves are converted into electric signals by detector.
  • The sonar device measures the time taken by ultrasound waves to travel from ship to bottom of sea and back to ship.
  • Half of this time gives the time taken by the ultrasound waves from ship to bottom.
  • Let the time interval between transmission and reception of
    ultrasound signal is t.
    Speed of sound through sea water is v
    Total distance travelled by waves = 2d.
    Then, 2d = v × t.
    This is called echo ranging.
  • The sonar is used to find the depth of sea, to locate underwater hills, valleys, submarines, icebergs and sunken ships etc.
  • Bats fly in the dark night by emitting high pitched ultrasound waves which are reflected from the obstacle or prey and returned to bats ear.
  • The nature of reflection tells the bat where the obstacle or prey is and what it is like.

STRUCTURE OF HUMAN EAR

  • The ear consists of three parts: outer ear, middle ear and inner ear.
  • The ears are the sense organs which help us in hearing sound.
  • The outer ear is called pinna. It collects the sound from surroundings.
  • This sound passes through the auditory canal.
  • At the end of auditory canal, is a thin elastic membrane called ear drum or tympanic membrane.
  • The middle ear contains of three bones: hammer, anvil and stirrup linked with one another. Free end of hammer touches ear drum and that of stirrup linked with membrane of oval window of inner ear.
  • The lower part of middle ear has a narrow ‘Eustachian tube’.
  • The inner ear has a coiled tube called cochlea, which is connected with oval window.
  • Cochlea is filled with a liquid containing nerve cells.
  • Other side of cochlea is connected to auditory nerve which goes to brain.

WORKING OF HUMAN EAR

  • Pinna → Ear canal → Ear drum →Hammer → Anvil → Stirrup → Oval window → Cochlea → Auditory nerve → Brain
  • When compression of sound wave strikes the ear drum, the pressure on the outside of ear drum increases and pushes the ear drum inwards.
  • While during rarefaction ear drum moves outwards. Thus, ear drum starts vibrating back and forth.
  • These vibrations are increased by three bones and middle ear transmits these amplified pressure variations received from sound waves to inner ear.
  • In the inner ear the pressure variations are turned into electric signals by the cochlea.
  • These electric signals are sent to the brain via auditory nerve and the brain interprets them as sound.
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